1. Field of the Invention
The present invention relates to a seat back frame which constructs a rear backbone of seats installed in a vehicle such as a car, the seat back frame having a frame body in which a pair of side frames to support a driver from both sides thereof are arranged between an upper frame and a lower frame. In particular, the present invention relates to a seat back frame in which at least an upper frame part and a pair of side frames can be formed by pressing treatment and bending treatment of a flat frame plate.
2. Description of Related Art
Conventionally, it is proposed various seat back frames. For instance, a seat back frame in which a pair of side frames are arranged between an upper frame and a lower frame, both being formed in a frame body, is well-known as shown in FIG. 20.
Here, conventional seat back frame will be described referring to FIG. 20. FIG. 20 is a perspective view of a conventional seat back frame. In FIG. 20, a seat back frame 100 is essentially constructed from a frame body 101 in which both an upper frame 102 (the frame positioned at upper side in FIG. 20) and a lower frame 103 (the frame positioned at lower side in FIG. 20) are formed into one body and a pair of side frames 104 each of which is fixed to the left and the right upper frames, respectively.
In the seat back frame 100, the frame body 101 is formed into a predetermined shape, which is substantially square shape and symmetrical at right and left, by bending a hollow pipe at first bending portions 101A, second bending portions 101B and third bending portions 101C. And in the thus formed frame body 101, the upper frame 102 is constructed from an upper part of the frame body 101 than the third bending parts 101C and the lower frame 103 is constructed from a pair of lower pipes 103 A, 103B which are bent toward inner directions at each of the third bending portions 101C. And each end portion of the lower pipes 103A, 103B are mutually faced to and fixed by welding.
And the side frames 104 are formed by fixing both ends of a pair of support wires to the upper frame 102 at positions mutually facing therein through welding. The side frames 104 are formed to support the driver form both sides of the seat back frame 100.
Further, at lower position of the right side frame 104 in FIG. 20 (the right lower position of the upper frame 102), a reclining bracket 105 for connecting a reclining device (not shown) is fixed by welding. And similarly, at the left lower position of the left side frame 104 (the left lower position of the upper frame 102), a hinge plate 106 is fixed by welding, the hinge plate 106 comprising a hinge which is utilized for reclining the seat back frame 100 in cooperation with the reclining device.
On inner sides of the upper frame 102 on which each of the side frames 104 is arranged, two pairs of spring clamps 108 are fixed by welding, the spring clamps 108 being used for installing S-shaped springs 107 which elastically support a cushion pad (not shown). And two S-shaped springs 107 are installed between two pairs of the spring clamps 108. Further, one more S-shaped spring 107 is installed between a pair of spring clamps 109 (only one spring clamp 109 is shown in FIG. 20), each of the spring clamps 109 being formed with the hinge plate 106 and the reclining bracket 105, respectively.
On the upper horizontal part of the upper frame 102 in the frame body 101, a pair of head-rest brackets 110 for installing head-rests (not shown) are fixed by welding.
Next, process for producing the above constructed seat back frame 100 will be given. First, to form the frame body 101, a hollow pipe is bent at the first, the second and the third bending portions 101A, 101B and 101C so that the frame body 101 becomes symmetrical at right and left therein. At this time, the hollow pipe concludes to be bent at six bending portions. And end portions of the lower pipes 103A, 103B which are innerly bent are contacted with each other and thereafter fixed by welding. Thereby, the frame body 101 is formed.
Further, at positions being opposed with each other in the upper frame 102 of the frame body 101, two pairs of spring clamps 108 and a pair of side frames 104 are fixed by spot welding, respectively. And the reclining bracket 105 is fixed by arc welding at the right lower position of the upper frame 102 and the hinge plate 106 is fixed by welding at the left lower position of the upper frame 102. Thereafter, on the upper horizontal part of the upper frame 102 in the frame body 101, a pair of head-rest brackets 110 are fixed by welding.
After the above, two S-shaped springs 107 are installed between the pairs of the spring clamps 108 and one more S-shaped spring 107 is installed between the spring clamps 109 each of which is formed with the hinge plate 106 and the reclining bracket 105, respectively. Thereby, the seat back frame 100 is completed. However, in the conventional seat back frame 100 mentioned above, it is necessary many members, each being formed independently from the frame bode 101, to be fixed to the frame body 101 in order to form the seat back frame 100. For instance, a pair of the side frames 104, the reclining bracket 105, the hinge plate 106 and the spring clamps 108 are necessitated for the seat back frame 100. Therefore, number of the members necessary to construct the seat back frame 100 becomes more and more and thus, total cost of the seat back frame 100 becomes very expensive by summing up costs of the members.
And since each member such as the side frames, etc. is fixed to the frame body 101 by welding, many welding processes are necessary to assemble the seat back frame 100. Thus, assembling cost of the seat back frame 100 becomes very expensive, as a result, there is a problem that cost of the seat back frame 100 is further increased in addition to costs for many members.
Further, in the seat back frame 100, it is necessary to fix each of the members at many positions in the frame body 101 by welding. Thus, since number of welding positions in the frame body 101 is increased it is very difficult to retain precise relations among the members so that each of the members is precisely connected to the frame body 101 with each other. As a result, when the seat back frame 100 is connected to the reclining device there will occur a trouble that rotating operation of the reclining device cannot be smoothly conducted based on connecting error which inevitably occurs among the members.
And in addition to the conventional seat back frame 100 shown in FIG. 20, it is disclosed a seat for vehicle in Japanese Utility Model Application after substantive examination, laid open No. Hei 3-21,638. In the seat for vehicle, a pair of side frame plates are fixed at side positions in a seat back frame and zigzag springs are installed between two pairs of spring clamps each of which is arranged on an inner side of the side frame plate, respectively. Further, on one of the side frame plates, a hinge plate for connecting a reclining device is fixed.
However, in the above seat for vehicle disclosed in Japanese Utility Model Application, the side frame plates, the spring clamps and the hinge plate are independently constructed with each other from the seat back frame. Thus, it is necessary to fix members such as the side frame plates, etc. to the seat back frame by welding, as a result, there still exist problems as same as those described in the above.
Furthermore, it is disclosed another seat back frame in Japanese Utility Model Application after substantive examination, laid open No. Hei 3-50,785. In such seat back frame, a frame backbone of the seat back frame is constructed by connecting a pair of side frames, each of which is formed from a flat plate, through spot welding and S-shaped springs are installed between holes to hook thereof, each hole being opened in the side frame.
However, in the seat back frame disclosed in the above Japanese Utility Model Application, though total number of the members necessary for constructing the seat back frame is reduced, each side frame is independently formed and it is necessary to mutually connect each of the side frames by spot welding. Therefore, it cannot be totally obtained enough strength by the above seat back frame and cost thereof cannot be reduced since the side frames have to be connected by spot welding and thus producing cost is increased. Further, an upper frame part of the seat back frame which is constructed by connecting each of the side frames is formed in a state of flat plate. Based on this construction, the upper frame part cannot retain enough strength against twisting moment loaded on the seat back frame. As a result, there is a problem that the seat back frame is easily twisted when driver's weight is loaded on the upper right portion or the upper left portion of the seat back frame through his hand(s).